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1.
Testing the relative performances of the single ring pressure infiltrometer (PI) and simplified falling head (SFH) techniques to determine the field saturated soil hydraulic conductivity, Kfs, at the near point scale may help to better establish the usability of these techniques for interpreting and simulating hydrological processes. A sampling of 10 Sicilian sites showed that the measured Kfs was generally higher with the SFH technique than the PI one, with statistically significant differences by a factor varying from 3 to 192, depending on the site. A short experiment with the SFH technique yielded higher Kfs values because a longer experiment with the PI probably promoted short‐term swelling phenomena reducing macroporosity. Moreover, the PI device likely altered the infiltration surface at the beginning of the run, particularly in the less stable soils, where soil particle arrangement may be expected to vary upon wetting. This interpretation was supported by a soil structure stability index, SSI, and also by the hydraulic conductivity data obtained with the tension infiltrometer, i.e. with a practically negligible disturbance of the sampled soil surface. In particular, a statistically significant, increasing relationship with SSI and an unsaturated conductivity greater than the saturated one were only detected for the Kfs data obtained with the PI. The SFH and PI techniques should be expected to yield more similar results in relatively rigid porous media (low percentages of fine particles and structurally stable soils) than in soils that modify appreciably their particle arrangement upon wetting. The simultaneous use of the two techniques may allow to improve Kfs determination in soils that change their hydrodynamic behaviour during a runoff producing rainfall event. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

2.
Field‐saturated soil hydraulic conductivity, Kfs, is highly variable. Therefore, interpreting and simulating hydrological processes, such as rainfall excess generation, need a large number of Kfs data even at the plot scale. Simple and reasonably rapid experiments should be carried out in the field. In this investigation, a simple infiltration experiment with a ring inserted shortly into the soil and the estimation of the so‐called α* parameter allowed to obtain an approximate measurement of Kfs. The theoretical approach was tested with reference to 149 sampling points established on Burundian soils. The estimated Kfs with the value of first approximation of α* for most agricultural field soils (α* = 0.012 mm?1) differed by a practically negligible maximum factor of two from the saturated conductivity obtained by the complete Beerkan Estimation of Soil Transfer parameters (BEST) procedure for soil hydraulic characterization. The measured infiltration curve contained the necessary information to obtain a site‐specific prediction of α*. The empirically derived α* relationship gave similar results for Kfs (mean = 0.085 mm s?1; coefficient of variation (CV) = 71%) to those obtained with BEST (mean = 0.086 mm s?1; CV = 67%), and it was also successfully tested with reference to a few Sicilian sampling points, since it yielded a mean and a CV of Kfs (0.0094 mm s?1 and 102%, respectively) close to the values obtained with BEST (mean = 0.0092 mm s?1; CV = 113%). The developed method appears attractive due to the extreme simplicity of the experiment. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

3.
Saturated hydraulic conductivity (Ks) affects the soil hydrological process and is influenced by many factors that exhibit strong spatial variations. To accurately measure Ks and its scale, spatial variability and relationship with collapsing gullies, we analysed four double-ring infiltrometer diameters in three soil layers during in situ experiments designed to measure Ks in two typical collapsing gullies (three slope sites) in Tongcheng County of China. The results showed that Ks increased with increasing inner ring diameter, but no significant difference existed between inner diameters of 30 and 40 cm. The Ks in red soil layers was higher than that in sandy soil layers, the transition layers had the lowest values. Ks also varied with slope position, gradually decreasing with distance from the gully head. The suggestion is that the spatial variation in Ks is affected not only by the intrinsic soil properties but also by the interaction with the collapsing gully.  相似文献   

4.
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5.
Biocrust effects on soil infiltration have attracted increasing attention in dryland ecosystems, but their seasonal variations in infiltrability have not yet been well understood. On the Chinese Loess Plateau, soil infiltrability indicated by saturated hydraulic conductivity (Ks) of biocrusts and bare soil, both on aeolian sand and loess soil, was determined by disc infiltrometer in late spring (SPR), midsummer (SUM), and early fall (FAL). Then their correlations with soil biological and physiochemical properties and water repellency index (RI) were analysed. The results showed that the biocrusts significantly decreased Ks both on sand during SPR, SUM, and FAL (by 43%, 66%, and 35%, respectively; P < .05) and on loess (by 42%, 92%, and 10%, respectively; P <.05). As compared with the bare soil, the decreased Ks in the biocrusted surfaces was mostly attributed to the microorganism biomass and also to the increasing content of fine particles and organic matter. Most importantly, both the biocrusts and bare soil exhibited significant (F ≥ 11.89, P ≤ .003) seasonal variations in Ks, but their patterns were quite different. Specifically, the Ks of bare soil gradually decreased from SPR to SUM (32% and 42% for sand and loess, respectively) and FAL (29% and 39%); the Ks of biocrusts also decreased from SPR to SUM (59% and 92%) but then increased in FAL (36% and 588%). Whereas the seasonal variations in Ks of the biocrusts were closely correlated with the seasonal variations in RI, the RI values were not high enough to point at hydrophobicity. Instead of that, the seasonal variations of Ks were principally explained by the changes in the crust biomass and possibly by the microbial exopolysaccharides. We conclude that the biocrusts significantly decreased soil infiltrability and exhibited a different seasonal variation pattern, which should be carefully considered in future analyses of hydropedological processes.  相似文献   

6.
Simulation of soil moisture content requires effective soil hydraulic parameters that are valid at the modelling scale. This study investigates how these parameters can be estimated by inverse modelling using soil moisture measurements at 25 locations at three different depths (at the surface, at 30 and 60 cm depth) on an 80 by 20 m hillslope. The study presents two global sensitivity analyses to investigate the sensitivity in simulated soil moisture content of the different hydraulic parameters used in a one‐dimensional unsaturated zone model based on Richards' equation. For estimation of the effective parameters the shuffled complex evolution algorithm is applied. These estimated parameters are compared to their measured laboratory and in situ equivalents. Soil hydraulic functions were estimated in the laboratory on 100 cm3 undisturbed soil cores collected at 115 locations situated in two horizons in three profile pits along the hillslope. Furthermore, in situ field saturated hydraulic conductivity was estimated at 120 locations using single‐ring pressure infiltrometer measurements. The sensitivity analysis of 13 soil physical parameters (saturated hydraulic conductivity (Ks), saturated moisture content (θs), residual moisture content (θr), inverse of the air‐entry value (α), van Genuchten shape parameter (n), Averjanov shape parameter (N) for both horizons, and depth (d) from surface to B horizon) in a two‐layer single column model showed that the parameter N is the least sensitive parameter. Ks of both horizons, θs of the A horizon and d were found to be the most sensitive parameters. Distributions over all locations of the effective parameters and the distributions of the estimated soil physical parameters from the undisturbed soil samples and the single‐ring pressure infiltrometer estimates were found significantly different at a 5% level for all parameters except for α of the A horizon and Ks and θs of the B horizon. Different reasons are discussed to explain these large differences. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

7.
The repellency index (RI) defined as the adjusted ratio between soil‐ethanol, Se, and soil‐water, Sw, sorptivities estimated from minidisk infiltrometer experiments has been used instead of the widely used water drop penetration time and molarity of ethanol drop tests to assess soil water repellency. However, sorptivity calculated by the usual early‐time infiltration equation may be overestimated as the effects of gravity and lateral capillary are neglected. With the aim to establish the best applicative procedure to assess RI, different approaches to estimate Se and Sw were compared that make use of both the early‐time infiltration equation (namely, the 1 min, S1, and the short‐time linearization approaches), and the two‐term axisymmetric infiltration equation, valid for early to intermediate times (namely, the cumulative linearization and differentiated linearization approaches). The dataset included 85 minidisk infiltrometer tests conducted in three sites in Italy and Spain under different vegetation habitats (forest of Pinus pinaster and Pinus halepensis, burned pine forest, and annual grasses), soil horizons (organic and mineral), postfire treatments, and initial soil water contents. The S1 approach was inapplicable in 42% of experiments as water infiltration did not start in the first minute. The short‐time linearization approach yielded a systematic overestimation of Se and Sw that resulted in an overestimation of RI by a factor of 1.57 and 1.23 as compared with the cumulative linearization and differentiated linearization approaches. A new repellency index, RIs, was proposed as the ratio between the slopes of the linearized data for the wettable and hydrophobic stages obtained by a single water infiltration test. For the experimental conditions considered, RIs was significantly correlated with RI and WDPT. Compared with RI, RIs includes information on both soil sorptivity and hydraulic conductivity and, therefore, it can be considered more physically linked to the hydrological processes affected by soil water repellency.  相似文献   

8.
The Beerkan method based on in situ single‐ring water infiltration experiments along with the relevant specific Beerkan estimation of soil transfer parameters (BEST) algorithm is attractive for simple soil hydraulic characterization. However, the BEST algorithm may lead to erroneous or null values for the saturated hydraulic conductivity and sorptivity especially when there are only few infiltration data points under the transient flow state, either for sandy soil or soils in wet conditions. This study developed an alternative algorithm for analysis of the Beerkan infiltration experiment referred to as BEST‐generalized likelihood uncertainty estimation (GLUE). The proposed method estimates the scale parameters of van Genuchten water retention and Brooks–Corey hydraulic conductivity functions through the GLUE methodology. The GLUE method is a Bayesian Monte Carlo parameter estimation technique that makes use of a likelihood function to measure the goodness‐of‐fit between modelled and observed data. The results showed that using a combination of three different likelihood measurements based on observed transient flow, steady‐state flow and experimental steady‐state infiltration rate made the BEST‐GLUE procedure capable of performing an efficient inverse analysis of Beerkan infiltration experiments. Therefore, it is more applicable for a wider range of soils with contrasting texture, structure, and initial and saturated water content. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

9.
ABSTRACT

The effects of topsoil addition of rice-husk dust (RHD) and cattle dung (CD), alongside surface mulching with dry grasses/legume, on the infiltration characteristics and intrinsic structural properties of a deep, well-drained soil in southeastern Nigeria are assessed. Treatments are RHD-amended, CD-amended and “unamended”, each plot being either surface-mulched or left bare, with the unamended-bare plots as control. Amendments and mulch were applied at 20 t/ha equivalents. Their effects on the soil’s infiltration characteristics 7 months later were not evident; however, there was a tendency for differences: CD-amended ≥ RHD-amended ≥ unamended and surface-mulched ≥ bare-surface. By contrast, saturated hydraulic conductivity (Ks ) differed thus: CD-mulched ≥ unamended-mulched > the rest. Similar values were recorded for Ks (50.89 cm/h) and final infiltration rate (50.74 cm/h) only under CD-amended plots, which also showed the highest values (43.50 cm/h) for transmissivity of the soil. Soil penetrometer resistance was lowest in CD-amended plots (113.44 kPa) and highest in unamended plots (166.78 kPa). Topsoil addition of cattle dung and surface mulching could increase infiltration, though marginally, and permeability of coarse-textured tropical soils beyond the season of their application when their effects on soil structure have almost waned.  相似文献   

10.
The saturated hydraulic conductivity, Ks, is a soil property that has a key role in the partitioning of rainfall into surface runoff and infiltration. The commonly used instruments and methods for in situ measurements of Ks have frequently provided conflicting results. Comparison of Ks estimates obtained by three classical devices—namely, the double ring infiltrometer (DRI), the Guelph version of the constant‐head well permeameter (GUELPH‐CHP) and the CSIRO version of the tension permeameter (CSIRO‐TP) is presented. A distinguishing feature in this study is the use of steady deep flow rates, obtained from controlled rainfall–runoff experiments, as benchmark values of Ks at local and field‐plot scales, thereby enabling an assessment of these methods in reliably reproducing repeatable values and in their capability of determining plot‐scale variation of Ks. We find that the DRI grossly overestimates Ks, the GUELPH‐CHP gives conflicting estimates of Ks with substantial overestimation in laboratory experiments and underestimation at the plot scale, whereas the CSIRO‐TP yields average Ks values with significant errors of 24% in the plot scale experiment and 66% in laboratory experiments. Although the DRI would likely yield a better estimate of the nature of variability than the GUELPH‐CHP and CSIRO‐TP, a separate calibration may be warranted to correct for the overestimation of Ks values. The reasons for such discrepancies within and between the measurement methods are not yet fully understood and serve as motivation for future work to better characterize the uncertainty associated with individual measurements of Ks using these methods and the characterization of field scale variability from multiple local measurements.  相似文献   

11.
Abstract

The accuracy of six combined methods formed by three commonly-used soil hydraulic functions and two methods to determine soil hydraulic parameters based on a soil hydraulic parameter look-up table and soil pedotransfer functions was examined for simulating soil moisture. A novel data analysis and modelling approach was used that eliminated the effects of evapotranspiration so that specific sources of error among the six combined methods could be identified and quantified. By comparing simulated and observed soil moisture at six sites of the USDA Soil Climate Analysis Network, we identified the optimal soil hydraulic functions and parameters for predicting soil moisture. Through sensitivity tests, we also showed that adjusting only the soil saturated hydraulic conductivity, Ks , is insufficient for representing important effects of macropores on soil hydraulic conductivity. Our analysis illustrates that, in general, soil hydraulic conductivity is less sensitive to Ks than to the soil pore-size distribution parameter.

Editor D. Koutsoyiannis; Associate editor D. Hughes

Citation Pan, F., McKane, R.B. and Stieglitz, M., 2012. Identification of optimal soil hydraulic functions and parameters for predicting soil moisture. Hydrological Sciences Journal, 57 (4), 723–737.  相似文献   

12.
The distribution of soil hydraulic and physical properties strongly influences runoff processes in landscapes. Although much work has been done to quantify and predict the properties of hillslope soils, far less is known about the distribution of soil properties in valley floors. A technique that links the estimation and distribution of soil hydraulic properties in valleys, with easily identified geomorphic features, was developed along a 2 km length of a valley at Brooks Creek in New South Wales, Australia. Soil physical and hydraulic property data were collected across a set of floodplain and fan features within the valley and analysed statistically to determine if soil properties varied significantly between geomorphic features and stratigraphic layers. The results show that the depth‐averaged saturated hydraulic conductivity, Ks, of the soil varies significantly with landform: fan units have Kg values that are twice that of floodplains and colluvial toeslope deposits have Ks values four times higher than floodplains. Given the notorious variability of Ks values in space, the strong statistical separation of soil properties by landform, backed up by strong separation of soil particle size by landform, suggests a way forward in understanding the distribution of soil properties in valleys and their influence on catchment hydrology. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

13.
Post‐wildfire runoff was investigated by combining field measurements and modelling of infiltration into fire‐affected soils to predict time‐to‐start of runoff and peak runoff rate at the plot scale (1 m2). Time series of soil‐water content, rainfall and runoff were measured on a hillslope burned by the 2010 Fourmile Canyon Fire west of Boulder, Colorado during cyclonic and convective rainstorms in the spring and summer of 2011. Some of the field measurements and measured soil physical properties were used to calibrate a one‐dimensional post‐wildfire numerical model, which was then used as a ‘virtual instrument’ to provide estimates of the saturated hydraulic conductivity and high‐resolution (1 mm) estimates of the soil‐water profile and water fluxes within the unsaturated zone. Field and model estimates of the wetting‐front depth indicated that post‐wildfire infiltration was on average confined to shallow depths less than 30 mm. Model estimates of the effective saturated hydraulic conductivity, Ks, near the soil surface ranged from 0.1 to 5.2 mm h?1. Because of the relatively small values of Ks, the time‐to‐start of runoff (measured from the start of rainfall), tp, was found to depend only on the initial soil‐water saturation deficit (predicted by the model) and a measured characteristic of the rainfall profile (referred to as the average rainfall acceleration, equal to the initial rate of change in rainfall intensity). An analytical model was developed from the combined results and explained 92–97% of the variance of tp, and the numerical infiltration model explained 74–91% of the variance of the peak runoff rates. These results are from one burned site, but they strongly suggest that tp in fire‐affected soils (which often have low values of Ks) is probably controlled more by the storm profile and the initial soil‐water saturation deficit than by soil hydraulic properties. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.  相似文献   

14.
The hydraulic properties of the topsoil control the partition of rainfall into infiltration and runoff at the soil surface. They must be characterized for distributed hydrological modelling. This study presents the results of a field campaign documenting topsoil hydraulic properties in a small French suburban catchment (7 km2) located near Lyon, France. Two types of infiltration tests were performed: single ring infiltration tests under positive head and tension‐disk infiltration using a mini‐disk. Both categories were processed using the BEST—Beerkan Estimation of Soil Transfer parameters—method to derive parameters describing the retention and hydraulic conductivity curves. Dry bulk density and particle size data were also sampled. Almost all the topsoils were found to belong to the sandy loam soil class. No significant differences in hydraulic properties were found in terms of pedologic units, but the results showed a high impact of land use on these properties. The lowest dry bulk density values were obtained in forested soils with the highest organic matter content. Permanent pasture soils showed intermediate values, whereas the highest values were encountered in cultivated lands. For saturated hydraulic conductivity, the highest values were found in broad‐leaved forests and small woods. The complementary use of tension‐disk and positive head infiltration tests highlighted a sharp increase of hydraulic conductivity between near saturation and saturated conditions, attributed to macroporosity effect. The ratio of median saturated hydraulic conductivity to median hydraulic conductivity at a pressure of − 20 mm of water was about 50. The study suggests that soil texture, such as used in most pedo‐transfer functions, might not be sufficient to properly map the variability of soil hydraulic properties. Land use information should be considered in the parameterizations of topsoil within hydrological models to better represent in situ conditions, as illustrated in the paper. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

15.
Saturated soil hydraulic conductivity, K s , data collected by ponding infiltrometer methods and usual experimental procedures could be unusable for interpreting field hydrological processes and particularly rainfall infiltration. The K s values determined by an infiltrometer experiment carried out by applying water at a relatively large distance from the soil surface could however be more appropriate to explain surface runoff generation phenomena during intense rainfall events. In this study, a link between rainfall simulation and ponding infiltrometer experiments was established for a sandy‐loam soil. The height of water pouring for the infiltrometer run was chosen, establishing a similarity between the gravitational potential energy of the applied water, E p , and the rainfall kinetic energy, E k . To test the soundness of this procedure, the soil was sampled with the Beerkan estimation of soil transfer parameters procedure of soil hydraulic characterization and two heights of water pouring (0.03 m, i.e., usual procedure, and 0.34 m, yielding E p  = E k ). Then, a comparison between experimental steady‐state infiltration rates, i sR , measured with rainfall simulation experiments determining runoff production and K s values for the two water pouring heights was carried out in order to discriminate between theoretically possible (i sR  ≥ K s ) and impossible (i sR  < K s ) situations. Physically possible K s values were only obtained by applying water at a relatively large distance from the soil surface, because i sR was equal to 20.0 mm h?1 and K s values were 146.2–163.9 and 15.2–18.7 mm h?1 for a height of water pouring of 0.03 and 0.34 m, respectively. This result suggested the consistency between Beerkan runs with a high height of water pouring and rainfall simulator experiments. Soil compaction and mechanical aggregate breakdown were the most plausible physical mechanisms determining reduction of K s with height. This study demonstrated that the height from which water is poured onto the soil surface is a key parameter in infiltrometer experiments and can be adapted to mimic the effect of high intensity rain on soil hydraulic properties.  相似文献   

16.
Determination of saturated hydraulic conductivity, Ks, and the van Genuchten water retention curve θ(h) parameters is crucial in evaluating unsaturated soil water flow. The aim of this work is to present a method to estimate Ks, α and n from numerical analysis of an upward infiltration process at saturation (Cap0), with (Cap0 + h) and without (Cap0) an overpressure step (h) at the end of the wetting phase, followed by an evaporation process (Evap). The HYDRUS model as well as a brute-force search method were used for theoretical loam soil parameter estimation. The uniqueness and the accuracy of solutions from the response surfaces, Ks–n, α–n and Ks–α, were evaluated for different scenarios. Numerical experiments showed that only the Cap0 + Evap and Cap0 + h + Evap scenarios were univocally able to estimate the hydraulic properties. The method gave reliable results in sand, loam and clay-loam soils.  相似文献   

17.
We collected soil‐hydraulic property data from the literature for wildfire‐affected soils, ash, and unburned soils. These data were used to calculate metrics and timescales of hydrologic response related to infiltration and surface runoff generation. Sorptivity (S) and wetting front potential (Ψf) were significantly different (lower) in burned soils compared with unburned soils, whereas field‐saturated hydraulic conductivity (Kfs) was not significantly different. The magnitude and duration of the influence of capillarity during infiltration was greatly reduced in burned soils, causing faster ponding times in response to rainfall. Ash had large values of S and Kfs but moderate values of Ψf, compared with unburned and burned soils, indicating ash has long ponding times in response to rainfall. The ratio of S2/Kfs was nearly constant (~100 mm) for unburned soils but more variable in burned soils, suggesting that unburned soils have a balance between gravity and capillarity contributions to infiltration that may depend on soil organic matter, whereas in burned soils the gravity contribution to infiltration is greater. Changes in S and Kfs in burned soils act synergistically to reduce infiltration and accelerate and amplify surface runoff generation. Synthesis of these findings identifies three key areas for future research. First, short timescales of capillary influences on infiltration indicate the need for better measurements of infiltration at times less than 1 min to accurately characterize S in burned soils. Second, using parameter values, such as Ψf, from unburned areas could produce substantial errors in hydrologic modeling when used without adjustment for wildfire effects, causing parameter compensation and resulting underestimation of Kfs. Third, more thorough measurement campaigns that capture soil‐structural changes, organic matter impacts, quantitative water repellency trends, and soil‐water content along with soil‐hydraulic properties could drive the development of better techniques for numerically simulating infiltration in burned areas.  相似文献   

18.
This study first explores the role of spatial heterogeneity, in both the saturated hydraulic conductivity Ks and rainfall intensity r, on the integrated hydrological response of a natural slope. On this basis, a mathematical model for estimating the expected areal‐average infiltration is then formulated. Both Ks and r are considered as random variables with assessed probability density functions. The model relies upon a semi‐analytical component, which describes the directly infiltrated rainfall, and an empirical component, which accounts further for the infiltration of surface water running downslope into pervious soils (the run‐on effect). Monte Carlo simulations over a clay loam soil and a sandy loam soil were performed for constructing the ensemble averages of field‐scale infiltration used for model validation. The model produced very accurate estimates of the expected field‐scale infiltration rate, as well as of the outflow generated by significant rainfall events. Furthermore, the two model components were found to interact appropriately for different weights of the two infiltration mechanisms involved. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

19.
The correct use of the tension disc infiltrometer requires the membrane of the disc base to be completely in contact with the soil surface. To achieve this contact, a thick layer of sand is commonly placed between the soil surface and the disc base. This paper presents an alternative disc (MDB), which, by incorporating a malleable membrane, allows direct infiltration measurements without using a contact sand layer. Infiltration curves obtained with this new design in a soil under three different tillage management treatments were compared with the corresponding curves obtained with a conventional disc (CDB) that uses a contact sand layer. The cumulative infiltration curves measured with CDB were analysed by the differentiated linearization (DL) method, and the corresponding curves obtained with MDB were analysed using both the DL and the cumulative linearization (CL) models. The values of hydraulic conductivity (K0) and sorptivity (S0) estimated with CDB were also compared with those obtained with MDB. Finally, the cumulative infiltration curves measured with CDB and MDB were compared with the corresponding modelled function for the respective K0 and S0 values calculated with the CL and DL models. The results show that, compared with CDB without a contact sand layer, MDB allows complete soil surface wetting even when non‐smoothed soil surfaces are used. The CDB, which yielded average K0 values 18% lower than those estimated with MDB, gave the highest values of standard error for the hydraulic parameters calculated. Furthermore, the subjective method employed in the CDB‐DL technique, which requires the first points of the differential infiltration line corresponding to the sand layer to be manually removed, introduces additional uncertainties in estimating S0 and K0. Comparison between the modelled and measured infiltration curves demonstrates that the DL or CL methods applied to MDB gave excellent estimates of S0 and K0. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

20.
Field determined hydraulic and chemical transport properties can be useful for the protection of groundwater resources from land-applied chemicals. Most field methods to determine flow and transport parameters are either time or energy consuming and/or they provide a single measurement for a given time period. In this study, we present a dripper-TDR field method that allows measurement of hydraulic conductivity and chemical transport parameters at multiple field locations within a short time period. Specifically, the dripper-TDR determines saturated hydraulic conductivity (Ks), macroscopic capillary length (λc), immobile water fraction (θim/θ), mass exchange coefficient (α) and dispersion coefficient (Dm). Multiple dripper lines were positioned over five crop rows in a field. Background and step solutions were applied through drippers to determine surface hydraulic conductivity parameters at 44 locations and surface transport properties at 38 locations. The hydraulic conductivity parameters (Ks, λc) were determined by application of three discharge rates from the drippers and measurements of the resultant steady-state flux densities at the soil surface beneath each dripper. Time domain reflectometry (TDR) was used to measure the bulk electrical conductivity of the soil during steady infiltration of a salt solution. Breakthrough curves (BTCs) for all sites were determined from the TDR measurements. The Ks and λc values were found to be lognormally distributed with average values of 31.4 cm h−1 and 6.0 cm, respectively. BTC analysis produced chemical properties, θim/θ, α, and Dm with average values of 0.23, 0.0036 h−1, and 1220 cm2 h−1, respectively. The estimated values of the flow and transport parameters were found to be within the ranges of values reported by previous studies conducted at nearby field locations. The dripper TDR method is a rapid and useful technique for in situ measurements of hydraulic conductivity and solute transport properties. The measurements reported in this study give clear evidence to the occurrence of non-equilibrium water and chemical movement in surface soil. The method allows for quantification of non-equilibrium model parameters and preferential flow. Quantifying the parameters is a necessary step toward determining the influences of surface properties on infiltration, runoff, and vadose zone transport.  相似文献   

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